From:
http://www.microsoft.com/office/previous/xp/columns/itcolumn02.asp
Looks like you have this dual save feature on.
Users of Office XP who need to share documents with users of Office 95
should be instructed to employ the Office XP "dual-file save" feature to
provide bidirectional compatibility. This function is invoked by selecting
one of the following options from the drop-down list in the Save As dialog
box:
a.. Word 97-2002 & 6.0/95-RFT
b.. Microsoft Excel 97-2002 & 5.0/95
c.. PowerPoint 97-2002 & 95
As you can see by the file type name designation for each application,
saving a document with a dual-file save type provides a host of
opportunities for sharing files across Office versions.
For enterprises where file sharing is a common procedure, the dual-file save
type is so useful that you should consider using the Office Profile wizard
to standardize on dual-file saves when you deploy Office XP. You can also
use Group Policies (or System Policies for networks using Microsoft Windows
NT), after installation, to set this file save type as the default.
If file sharing is an issue only within small groups of users, those Office
XP users can be instructed to use the Options dialog to set the dual-file
save type as their default. Of course, even if you use the Office Profile
wizard, or Group Policies, users can change the default file type, but Group
Policies reset the default each time the user logs on. Users who don't need
to share documents with earlier versions will frequently correct the default
file type to Office XP, and if you've imposed a Group Policy that resets the
default file type with each logon, you've created an annoying work
environment. You must manage default file types with user needs in mind.
The dual-file save feature creates two data streams: one for the file format
and features of Office XP/2000/97; and one for the earlier versions. This
creates an efficient environment for document sharing. However, the multiple
data streams mean document files are doubled in size. After you have
completed your deployment of Office XP, you should instruct users to save
their files in the 2002 format, which will remove the additional data
required for earlier version use.
When users of earlier versions open files saved in the dual-file save
format, they are prompted to open the file as a Read Only document. Office
permits users to decline this offer, but saving the file in a version
earlier than Office 97 could remove some of the features available in Office
XP.
